Table 1 Strains, plasmids and protein used in this study

 S4074

A. pleuropneumoniae reference strain of serovar 1; WT strain

 ΔqseBC

A. pleuropneumoniae S4074 qseBC-deletion mutant

 ΔapfA

A. pleuropneumoniae S4074 apfA-deletion mutant

 ΔapfB

A. pleuropneumoniae S4074 apfB-deletion mutant

 ΔapfC

A. pleuropneumoniae S4074 apfC-deletion mutant

 ΔapfD

A. pleuropneumoniae S4074 apfD-deletion mutant

 CΔqseBC

Complemented strain of ΔqseBC; Cm^r

 CΔapfA

Complemented strain of ΔapfA; Cm^r

 CΔapfB

Complemented strain of ΔapfB; Cm^r

 CΔapfC

Complemented strain of ΔapfC; Cm^r

 CΔapfD

Complemented strain of ΔapfD; Cm^r

 DH5α

Cloning host for recombinant vector

 β2155

Transconjugation donor for constructing mutant strain

 BL21 (DE3)

The expression host for pET-30a and their derivative

 pEMOC2

Transconjugation vector: ColE1 ori mob RP4 sacB, Amp^r Cm^r

 pEΔqseBC

Up- and down-stream arms of qseBC were ligated sequentially into pEMOC2, and used as the transconjugation vector for qseBC gene deletion

 pEΔapfA

Up- and down-stream arms of apfA were ligated sequentially into pEMOC2, and used as the transconjugation vector for apfA gene deletion

 pEΔapfB

Up- and down-stream arms of apfB were ligated sequentially into pEMOC2, and used as the transconjugation vector for apfB gene deletion

 pEΔapfC

Up- and down-stream arms of apfC were ligated sequentially into pEMOC2, and used as the transconjugation vector for apfC gene deletion

 pEΔapfD

Up- and down-stream arms of apfD were ligated sequentially into pEMOC2, and used as the transconjugation vector for apfD gene deletion

 pJFF224-XN

E. coli-APP shuttle vector: RSF1010 replicon; mob oriV, Cm^r

 pJFF-qseBC

pJFF224-XN carrying the intact qseBC

 pJFF-apfA

pJFF224-XN carrying the intact apfA

 pJFF-apfB

pJFF224-XN carrying the intact apfB

 pJFF-apfC

pJFF224-XN carrying the intact apfC

 pJFF-apfD

pJFF224-XN carrying the intact apfD

 pET-30a

Expression vector; Kan^r

 pET-qseB

pET-30a carrying qseB gene